1. Field of the Invention
The present invention relates to a digitizing apparatus or digitizer to be used as an input device for computer equipment.
2. Description of the Related Art
FIG. 5 is a perspective diagram showing the structure of a digitizer as a digitizing apparatus and FIG. 6 is a block diagram showing its configuration.
A digitizer 1 has a display surface 2 and is connected to computer equipment via a cable 3. On the display surface 2 is displayed a picture 4 in accordance with picture information that is supplied from the computer equipment. By writing a characters or drawing a graphic on the display surface 2 using an input pen 5, the tracing is sent to the computer equipment at predetermined time intervals as coordinate information.
The digitizer 1 comprises a flat display 11, a resistance sheet 12, a display control circuit 13, a coordinate processing circuit 14, a picture memory 15, and a CPU 16. The flat display 11 is formed, for example, from a liquid crystal display (LCD) and positioned on the display surface 2 of the digitizer 1. The flat display 11 receives a picture signal Y together with a horizontal synchronization signal HD and a vertical synchronization signal VD, and displays a picture in accordance with the picture signal Y. The resistance sheet 12 is a pressure-sensitive transparent resistor that is positioned on the display surface 2 while overlapping the flat display 11. The resistance sheet 12 has, for example, a first sheet positioned with a resistance in the horizontal direction overlapping a second sheet positioned with a resistance in the vertical direction, and has its resistance value R change depending on the location receiving pressure.
The display control circuit 13 generates the picture signal Y on the basis of the picture data stored in the picture memory 15 as well as generates the horizontal synchronization signal HD and the vertical synchronization signal VD in synchronous with the picture signal Y, and supplies the picture signal Y, the horizontal synchronization signal HD, and the vertical synchronization signal VD to the flat display 11. The coordinate processing circuit 14 is connected to the resistance sheet 12, and detects on the basis of the resistance value R that is input from the resistance sheet 12 the coordinate of the position receiving pressure on the resistance sheet 12. In the coordinate processing circuit 14, the continuously changing coordinate is detected periodically by sampling the change in resistance value R at a fixed period. The coordinate is then continuously sent to a bus 10 as coordinate information following a predetermined format.
The picture memory 15 stores picture information one screen at a time supplied from the computer equipment that is connected to the digitizer 1 and supplies it to the display control circuit 13. The CPU 16 is, for example, a one-chip microcomputer, is connected via the bus 10 to the display control circuit 13, the coordinate processing circuit 14, and the picture memory 15, and controls the operation of each section in accordance with a predetermined control program. The bus 10 is connected to the computer equipment via an interface, and transfers information from the computer equipment to the picture memory 15 and the CPU 16 as well as transfers coordinate information from the coordinate processing circuit 14 to the computer equipment.
In the above-mentioned digitizer, the tracing drawn with the input pen 5 on the display surface 2 can be continuously converted into numeric values as coordinate information and the information can be loaded into the computer equipment.
In the above-mentioned digitizer, it is necessary to position the resistance sheet 12 so as to overlap the flat display 11. A problem arises in which the structure of the display surface 2 becomes complex. Furthermore, since the resistance sheet 12 has a plurality of sheets, a problem arises in which the display 11 becomes hard to see due to the influence of light interference.